As essential individual components of a rolling bearing, rolling bearing rings are exposed to considerable mechanical loads. Since the force transmission on the racetrack takes place due to frequency related stress the bearings must in each case be hardened. The last two steps in working these racetracks are the grinding and the honing.
The profile of the racetrack is put into final form by the grinding process. Generally, a circumferential grinding disk mounted on a tool spindle is disposed with its longitudinal axis parallel to the axis of symmetry of the rolling bearing ring to be worked. The circumference of this grinding disk has in its radial section a profile which corresponds to the negative of the profile to be worked into the track. If a grinding disk is positioned axially to the rolling bearing ring to be ground and then advanced radially while being rotated toward the rotating workpiece the desired racetrack profile is produced on the racetrack of the rolling bearing ring. The radial advance motion is stopped when the desired radial dimension of the racetrack profile is reached. Subsequently, the length of advance is traversed back in rapid motion, the worked workpiece is exchanged against an unworked workpiece, and a new working cycle can begin. From time to time the grinding disk which is subjected to continuous abrasion must be newly profiled between two working cycles. The most modern machines of this type today have tool spindles operating with a rotational speed of up to 180,000 revolutions per minute, the bearing ring to be worked rotating at approximately 1500 revolutions per minute, and the clock timer per working cycle is only a few seconds. The goal of their grinding process is providing the rolling bearing racetrack with its final form. Since their measuring accuracy is of utmost importance for the function and the operation of the rolling bearing, the advance motion must follow very precisely a given path function and must especially at its extreme point assume a geometrically exact position. Since all relative motions between tool and workpiece are path-bound the machine construction must be implemented to very small tolerance. For this reason so-called glide shoes have inter alia proven to be reliable for the support of the rotating workpiece. They represent a very rigid member in the force flow of the machine and therewith contribute significantly to the retention of the dimensional accuracy of the finished workpiece.
The surface generated by the grinding process is generally not sufficient for the running surface of the rolling bearing so that normally a honing process follows. In this fabrication step the basic working speed is achieved through the rotation of the workpiece about its axis of symmetry. A honing stone whose contact zone is adapted to the racetrack profile of the rolling bearing is pressed under a predetermined force onto the racetrack profile. In this manner through the contact points between workpiece and tool which shift continuously, the surface character assumes a uniform shape. Simultaneously, the abrasion generated on the honing stone is thereby made uniform such that its contour is retained to the largest possible extent. At the conclusion of the honing process, however, care must be taken because the honing traces in the final analysis are unavoidably extended in the direction of motion of the rolling elements and do not show any component perpendicular to it. For that reason the honing frequency is markedly reduced toward the end of the working process. The rotational speed of the workpiece can be varied and can reach up to 15,000 revolutions per minute. In contrast to the previously described grinding process the honing stone is guided in a manner which is not path-bound but rather force-bound. The requirement for a particularly rigid machine construction here becomes irrelevant. Instead a defined flexibility is required so that through the amount of the advance the working force can specifically be given. For this reason for the bearing of the rotating workpiece a defined flexible type of bearing is used wherein a hydrostatic glide bearing has proven useful. The feed introduced into this force flow has therein no decisive influence on the capacity to retain dimensional accuracy of the worked workpiece. However, it determines decisively the force effective in the working. Moreover, the hydrostatic glide bearing has the advantage that the residual waves unavoidably present in the external surface of the rolling bearing rings are averaged out in the best possible manner and the radial deviations of the workpiece resulting therefrom are largely reduced. This has especially advantageous effects on the noise behavior of the rolling bearing completed later. In the general case a single honing process is not sufficient for achieving the required surface quality so that normally the honing is divided into preliminary final honings wherein both individual steps are carried out according to the identical scheme, albeit with different tools.
The final working of the rolling bearing rings according to the current state of the art requires for each of the two fabrication steps "racetrack grinding" and "racetrack honing" one separate machine tool each. In this method serious disadvantages are encountered. Considerable investments with high costs are required. Furthermore, the racetrack-ground ring must be transported to the honing machine which requires additional expenditures. Especially in the case of material flow technology with linkage of the machines with each other considerable means of handling, transporting, and storage arrangements are involved. A further disadvantage of this known fabrication technology consists in that the rolling bearing rings, unsymmetrical with respect to their axial extension, are normally supported in any given orientation position between grinding and honing and on being placed into the honing machine must again be oriented into the correct position with respect to their axial orientation. While, with bearing rings which with respect to their central position are unsymmetrical this requirement is unavoidable, it is also to an increasing extent made with symmetrical rings since the rolling bearing ring even with highly precise working is never completely symemtrical. Since the grinding as well as the honing process refer to the same racetrack profile, for high precision fabrication it is advantageous if the ring leaving the grinding machine is honed in precisely the same axial orientation. If, in contrast, the ring is inserted arbitrarily with respect to its axial orientation, then the honing stone will not be able to follow the contour given by the grinding because of the symmetry of the rings, which is never complete. For this reason, even with rolling bearing rings with symmetrical nominal profile, placing these rings into the correct position into the honing machine is advantageous. However, this can only be realized with considerable expenditures and requires for example, especially in the case of small ring dimensions, a very expensive linkage of the successive grinding and honing machines.
Under these circumstances it is desirable to combine the process steps for the grinding and honing process in such a way that a workpiece is first ground and then honed in the same chucking. For the above-mentioned reasons this is not possible since the requirements made of the bearing of the workpiece are oppositely directed.